Flag summary

There follows a brief summary of the different flags taken by pgn-extract, such
as is produced by the -h flag. You are strongly advised to read the remainder
of this file, however, before attempting to use extract in earnest.

Flags:

-7 - output only the seven tag roster for each game. Other tags (apart
from FEN and possibly ECO/Opening/Variation) are discarded (See -e).

-aoutputfile - the file to which extracted games are to be appended.
See -o flag for overwriting an existing file.

-Aargsfile - read the program's arguments from argsfile.

-b[elu]num - restricted bounds on the number of moves in a game.

lnum set a lower bound of 'num' moves,

unum set an upper bound of 'num' moves,

otherwise num (or enum) means equal-to 'num' moves.

-cfile[.pgn] - Use file as a list of check files for duplicates.

-C - don't include comments in the output. Ordinarily these are retained.

-dduplicatefile - the file to which duplicate extracted games are
to be written.

-D - don't output duplicate extracted game scores.

-eECO_file - perform ECO classification of games. The optional
ECO_file should contain a PGN format list of ECO lines
Default is to use eco.pgn from the current directory.

-E[123 etc.] - split output into separate files according to ECO.

E1 : Produce files from ECO letter, A.pgn, B.pgn, ...

E2 : Produce files from ECO letter and first digit, A0.pgn, ...

E3 : Produce files from full ECO code, A00.pgn, A01.pgn, ...

Further digits may be used to produce non-standard further
refined division of games.

All files are opened in append mode.

-ffile_list - file_list contains the list of PGN files to be
searched - one per line.

-F - output a FEN string comment of the final game position.

-h - print an abbreviated list of help.

-h1 - print further help.

-? - print an abbreviated list of help.

-llogfile - Create a new logfile for the diagnostics rather than
using stderr.

-Llogfile - Append all diagnostics to logfile.

-M - Match only games which end in checkmate.

-noutputfile - Write all valid games not otherwise output to outputfile.

-N - don't include NAGs in the output. Ordinarily these are retained.

-ooutputfile - the file to which extracted games are to be written.
Any existing contents of the file are lost (see -a flag).

-P - don't match permutations of the textual variations (-v).

-r - report any errors but don't extract.

-Rtagorder - Use the tag ordering specified in the file tagorder.

-s - silent mode don't report each game as it is extracted.

-S - Use a simple soundex algorithm for tag matches. If used, this
option must precede the -t or -T options.

-ttagfile - file of player, date, or result, extraction criteria.

-Tcriterion - player, date, or result, extraction criteria.

-U - don't output games that only occur once. (Use with -d to
identify duplicates in multiple files.)

-V - don't include variations in the output. Ordinarily these are retained.

-wwidth - set width as an approximate line width for output.

-W - don't rewrite the moves into Standard Algebraic Notation.

-W[cm|epd|halg|lalg|elalg|san] - specify the output format to use.

Default (i.e., without this flag) is SAN.

-W (without anything following) selects the input format.

-Wcm is a legacy option that wrote ChessMaster format.
I don't know if the output produced is still valid.

-Wepd is EPD format.

-Whalg is hyphenated long algebraic.

-Wlalg is long algebraic

-Welalg[PNBRQK] is enhanced long algebraic. Use the characters
PNBRQK for language specific output, e.g: -WelalgBSLTDK for German.

-Wsan[PNBRQK] Use the characters PNBRQK for language
specific output, e.g: -WsanBSLTDK for German.

-xvariations - the file variations contains the lines resulting in
positions of interest.

-zendings - the file endings contains the end positions of interest.

-Z - use the file virtual.tmp as an external hash table for duplicates.
Use when MallocOrDie messages occur with big datasets.

-#num - output num games per file, to files named 1.pgn, 2.pgn, etc.

--checkmate - only output games that end in checkmate

--evaluation - include a position evaluation after each move

--nomovenumbers - don't output move numbers

--noresults - don't output results

--notags - don't output any tags.

--plylimit - limit the number of plies output.

--stalemate - only output games that end in stalemate

Error messages and verbose reporting is done to the standard error output unless
the -l/-L flag is used.

Usage and Arguments (-f)

Extract takes an arbitrary number of game scores as input and outputs
zero or more of these games, typically in English Standard Algebraic
Notation (SAN). Which of the input games are output, and the style
of the output, depend upon the particular set of command line flags
passed to pgn-extract.
The general form for calling pgn-extract is as follows:

pgn-extract [flags] [input-game-files]

In its simplest form, calling pgn-extract with no arguments will cause
it to read games from its standard input, check them and reproduce those
without errors in SAN notation on its standard output.

Normally, the input files from which games are to be extracted are listed on the
command line:

pgn-extract file1.pgn [file2.pgn ...]

An alternative to listing the game files on the command line is to list
their names, one per line, in a file which is then given after the -f flag:

pgn-extract -ffile_list

In order to save the output in a file rather than standard output,
use either -o or -a to indicate the output
file name, for instance:

Input Format

This program's principle aim is to be able to read PGN files and output
games of interest. It follows that the input should look reasonably like PGN to
start with. This means that it doesn't cope well with files that
contain news article or mail headers, for instance, although it does
make an attempt to skip text that is obviously not game related between
games. Having said that, it does not require the move text be in
Standard Algebraic Notation (SAN). It will accept quite a few common
formats including:

Algebraic

Long Algebraic

various commonly-used intervening characters, such as : - x

Dutch and German upper case piece letters.
(Support for Russian piece letters is in prototype.)

lower-case English piece characters (except that it will always prefer
'b' to mean a pawn move rather than a Bishop move).

It does not
require that there be any move numbers or PGN headers preceding a game,
as long as the move text is terminated by a valid result designation:
*, 1-0, 0-1, 1/2-1/2 (1/2 is also accepted).
This makes the program reasonably suitable for entering raw game text and
having it reformatted in proper SAN with a full set of headers.

Output Files (-o, -a)

In order to output all matched games to a single new file, the -o flag is used:

pgn-extract -onew.pgn file1.pgn file2.pgn

This has the effect of creating new.pgn from the contents of file1.pgn
and file2.pgn. The games
in both source files are checked and rewritten, if necessary, into SAN.
Any previous contents of new.pgn will be lost with the -o flag. In order to
avoid this and append to an existing file, use the -a flag:

pgn-extract -anew.pgn file1.pgn file2.pgn

Note that there should be no space between either -o or -a and the output file name.

Variations (-v and -x)

There are two distinct ways to specify variations of interest;
positional variations (the -x flag) and
textual variations (the -v flag).
The major difference between the two is that positional variations
specify a complete move sequence whose end position is the primary
point of interest, whereas textual variations allow incomplete and
fuzzy move sequence matches on the text of a game to select games.
Whilst it is possible to use both
flags together, this would be unusual as a game must match with both to
be extracted.

Positional Variations (-x)

The variations in which you are interested should be placed in a file
whose name is supplied with the -x flag. For instance:

pgn-extract -xvars

where each variation is
listed on a single line in the file vars (the filename is immaterial).
The following set of moves:

e4 c5 Nf3 d6 d4 cxd4 Nxd4 Nf6 Nc3 a6

indicates that you wish to pick up all games reaching the Najdorf
variation position of the Sicilian Defence.
Games reaching the end position of this sequence are
selected regardless of the route that was taken to reach it. This
allows various transpositional sequences to be specified by quoting
just one line to reach the required point. Therefore, games employing
the following move order will be picked up by quoting the line above.

e4 c5 Nc3 d6 Nge2 Nf6 d4 cxd4 Nxd4 a6

A position is considered to match a required variation if it generates
the same board hash value. In the interests of reasonable efficiency,
no attempt is made to actually examine the state
of the board. There is, therefore, the potential for false hits but in
my usage of pgn-extract I have not found this to be a problem.

With this option, games are only searched to a depth approximately equal
to the length of the longest positional variation, in order to make
processing of large data sets faster than with a search of the whole
game.

A comment line may be placed in a variation file by using a '%' as the
first character of the line. Move numbers are optional within the
list of moves.

Positional matches are also available using a FEN description of the
desired position.
See the description of the -t flag
for how to specify a FEN position,
and the -F flag
for a simple way to generate a FEN description from
a game score.

Textual Variations (-v)

With this option, the matching is purely textual in nature,
in contrast to the -x flag. The -v flag works by
string matching on the input text of moves,
so there is no facility for picking up transpositions automatically.
The variations in which you are interested should be placed in a file
whose name is supplied with the -v flag. For instance:

pgn-extract -vvars

Each variation should be listed on a single line
in the file vars (the filename is immaterial).
The move sequence:

e4 c5 Nf3 d6 d4 cxd4 Nxd4 Nf6 Nc3 a6

indicates that you wish to pick up all games following the normal move
order of the Najdorf variation of the Sicilian Defence, and

d4 Nf6 c4 e6 Nc3 Bb4

that you are interested in Nimzo-Indian games.
The order in which the moves are played by either White or Black
is immaterial. All combinations are tried, so the ordering:

c4 e6 Nc3 Bb4 d4 Nf6

will produce the same set of matches as the previous ordering of the
Nimzo-Indian moves (see the -P flag for how
to prevent this).

A comment line may be placed in a variation file by using a '%' as the
first character of the line. Move numbers are optional within the
list of moves.

As transpositions are not picked up automatically with this flag,
if you also wanted to
recognise the following as a Najdorf, you would have to add this line
to the variations file in addition to that given above:

e4 c5 Nc3 d6 Nge2 Nf6 d4 cxd4 Nxd4 a6

However, because of the way in which the matching is done, it is
possible to specify slight alternatives on the way in which individual
moves are written. Notational alternatives for a single move are just
written separated from each other with a non-move character. This
variation specifies both the shorter and longer ways of writing the
captures in a Najdorf:

e4 c5 Nf3 d6 d4 cxd4|cd Nxd4|Nd4 Nf6 Nc3 a6

However, given the variety of possible ways of writing various moves in
non-SAN format, e.g.

cxd4|cd|c5d4|c5-d4

variation lists can get quite messy and I believe that this approach is
best avoided by ensuring that the input is proper SAN and only using
SAN notation in the variations file. In this way, the alternative-separator
can then be used purely for indicating genuine alternative moves at
that point, e.g.

e4 c5 Nf3 d6 d4|d3

An important point when listing moves is that check and mate indicators
should be included where appropriate, otherwise moves incorporating
these characters in games to be searched will fail to match.

There is little point in using the -v flag in preference to
the -x flag
if you are only interested in finding games that reach a particular
position. The real use for -v is when you wish to pick up games
in a more general way. For instance, the character '*' may be used in
place of any move to indicate that you don't care what was played at
that point. So the following:

* b6

means that you are interested in all games in which Black replied
1 ... b6 regardless of White's first move.
The sequence:

d4 * c4 * Nc3 *

will pick up Nimzo-Indian, Grunfeld, King's Indian, etc. defences.
This notation is not possible with positional variations.

In addition, the character '!' may be used in front of any move to
indicate that you wish to disallow particular moves from matching at
this point. For instance, if you want to find Sicilian games where
White did not reply with Nf3 at move 2 you would specify:

e4 c5 !Nf3

If you wished to disallow 2.Ne2 as well then

e4 c5 !Nf3|Ne2

does the job. (Adding parentheses makes no difference as the '!' is
applied to all of the following move string.)

Care should be taken combining '!', '*' and variation permutations (see the -P flag).
Disallowed moves take precedence over '*' moves. If a single
disallowed move is found in a game within the length of the variation,
that game is excluded. This was the most sensible interpretation that
I could find to place on this usage.

Textual Variation Permutations (-P)

Normally, all permutations of a textual variation (see the -v flag) are tried against the
moves of a game. This cuts down on the number of separate
transpositional orderings that it is necessary to list, at the cost of
slower matching of each game. If the following were used to look for
Nimzo-Indian games:

d4 Nf6 c4 e6 Nf6 Nc3 Bb4

a side-effect would be that it will also pick up games which start as:

1. c4 Nf6 2. Nc3 e6 3. d4 Bb4

for instance.
The -P flag requests that textual variations are matched against the
moves of the game strictly in the order in which they are listed,
without trying different orders. So, if you want to find only those
games that follow a particular move order, use this flag to suppress
permutations.

Duplicate Games (-d and -D or --noduplicates, plus -Z)

If either the -d or -D flag is used, pgn-extract attempts to recognise
duplicate extracted games.
Using the -d flag indicates that you wish copies of the duplicate
games to be written to the indicated file:

pgn-extract -ddupes.pgn -ounique.pgn file.pgn

will extract from file.pgn the unique set of games into unique.pgn and
the duplicates (i.e., the second and subsequent copies of a game)
to dupes.pgn.
A comment identifying in which file a
duplicate was found precedes the first duplicate found in that file and
each duplicate game has a prefix comment indicating the file in which
the first version was found.

With the -D flag duplicate games are suppressed
from the output. These two flags are mutually exclusive, therefore.

Duplicates are identified by comparing a hash value for the board of
the end positions of extracted games and an additional cumulative hash
value generated from the move sequence.
If these both values match then games are considered to be
duplicates.
This is not guaranteed to be exact but it gives a good approximation.

You should note that games are only considered to be duplicates on the
basis of the moves played. It may be that a game considered to be a
duplicate contains annotations and variations not present in the one
found earlier, so it might be necessary to do some swapping around to
obtain those you really wish to retain. You should, therefore, use the
-D flag with caution if you are trying to reorganise your master
collection rather than selecting out specific games for examination.
(See also the -U flag.)

Detecting duplicates requires memory for the storage of a hash table
containing information on each game. No attempt is made to use
extended or expanded memory and so large databases can result in
a MallocOrDie error. If this is the case, try using the -Z flag which
forces pgn-extract to store its hash table externally, in a file called
virtual.tmp. Each game requires 16 bytes of file space. Clearly, if a
very large database is being processed, there is a risk of filling up
the available file space if there is insufficient available.

Suppression of Unique Games (-U or --nounique)

The -U flag suppresses output of the first occurrence of a particular
game. This is useful when combined with the -d flag
as a means of
identifying just those games that are duplicated in a list of multiple
files. As the duplicate games are commented with the file in which
they were located, it then becomes possible to prune a set of files
containing common games. For instance, suppose oldfile.pgn contains a
set of games without duplicates, and you wish to know which games in
newfile.pgn already occur in oldfile.pgn:

pgn-extract -U -ddupes.pgn oldfile.pgn newfile.pgn

will write to dupes.pgn the duplicate games so that you can go through
newfile.pgn and remove them. Of course, if you simply want to hold the
combined set of unique games in a single file you would use something like:

Check Files for Duplicates (-c)

Check files contain games that are to be used in duplicate detection,
but not to form part of the output. If the filename appended to the
argument has a .pgn/.PGN suffix it is assumed to be a single file of
games. If it does not have this suffix then it is assumed to be a file
containing a list of the names of PGN game files, one per line, to be
used as check files. A typical use for this is to select new games of
interest from a file that probably contains games that exist elsewhere.
In the following example, we wish to select Nimzo-Indian games from
newfile.pgn that don't already occur in the master file nimzo.pgn:

pgn-extract -cnimzo.pgn -vnimzo.var -D -onewnimzo.pgn newfile.pgn

The games in nimzo.pgn act as the source for duplicate detection so
duplicates of these will be suppressed (the -D flag).
Only those games from
newfile.pgn which are not in nimzo.pgn will be output to newnimzo.pgn.
Contrast this behaviour with the following, which would create a new
master file of games from the combination of nimzo.pgn and
newfile.pgn:

pgn-extract -vnimzo.var -D -onewnimzo.pgn nimzo.pgn newfile.pgn

Matching on Tag Criteria (-t)

There are two ways to specify that you wish to use information in the
tag fields as extraction criteria: the -t flag and
the -T flag. The -t flag takes a file name
argument and is the preferred method because of its ease of use and
greater flexibility:

pgn-extract -ttags games.pgn

where tags is an arbitrary file name.
In the file are listed tag name and value pairs
corresponding to the extraction criteria you wish to use.
Each line of this file should be of the form:

PGN-Tag-name Tag-string

for instance:

White "Tal"

(note the need to include double quotes around the tag value).
This requests that only those games where Tal had the White pieces are
to be considered for extraction.
If you wish to limit the year in
which those games were played you might list:

White "Tal"
Date "1962"

Multiple pairs with the same tag name are or-ed together so:

% Find games in the period 1960-1962.
Date "1960"
Date "1961"
Date "1962"

will select all games from the three listed years.
Note that comments may be included in the tag file.

In general, tags names that differ are and-ed together, so:

White "Tal"
Black "Fischer"
Date "1962"
Result "1-0"

selects only those games that Tal won with the White pieces against
Fischer in 1962.

It is important to note that:

White "Tal"
Black "Tal"

does not find all games played by Tal, but only those that he played
against himself. In order to overcome this, I have introduced a
non-PGN tag that should only be used in the extraction criteria file:

Player "Tal"
Date "1962"

finds all games from 1962 in which Tal had either the White pieces or
the Black. In effect, the White and Black player lists are or-ed
together rather than and-ed using this pseudo-tag.

Prefix matching on tag values is done so that a criterion should be a prefix
of the complete Tag string. Thus,

All tag criteria except ECO classification are checked before the moves
of the game in the interests of efficiency (tag checking is relatively
fast whereas positional checking of the game is not). Only once the
game has been processed is it checked to see whether an ECO tag match
has been requested. The consequence of this is that using the
-e flag
in combination with ECO tag criteria you can search for games in
particular ECO lines without an ECO tag having been present in the
input form.

Use of a FEN tag with the -t flag has
a special meaning. Rather than using this to match FEN tags in
the header of a game, a FEN description is used to indicate a search
for a positional match (similar to use of the -x flag).
If a FEN description is provided with the -t flag, the indicated
position is searched for in each game processed, and only those
games that reach the indicated position are output.
A FEN tag-pair for the starting position would be described by:

FEN "rnbqkbnr/pppppppp/8/8/8/8/PPPPPPPP/RNBQKBNR w KQkq - 0 1"

The position after the two moves e4 c5 would be:

FEN "rnbqkbnr/pp1ppppp/8/2p5/4P3/8/PPPP1PPP/RNBQKBNR w KQkq c6 0 2"

See details of the -F flag for a simple way to generate a FEN
description from a game score.

Date and Elo Matches with -t

From a -t tag file,
more complex matching of dates and Elo values may be performed by
placing an operator between the tag name and the tag string to be
matched:

Date < "1962"

would only match games played before 1962. Only the year value
participates in the matching process, as this is done using integer
values rather than strings.

WhiteElo >= "2500"

only matches games where White is a strong player. Probably of more
general use is another pseudo-tag that I have introduced purely for
this purpose: Elo.

Elo >= "2500"

matches games in which either player has an Elo tag matching that
relationship.
The operators allowed are >, >=, <, <=, =, and <> (not
equal to).

Tag Criteria on the Command Line (-T)

An alternative to the -t flag is the
-T flag, for use where command line arguments are
more convenient - perhaps where pgn-extract is being invoked from another
program. The tag coverage is not as extensive as with a tag file, and
the syntax is rather cumbersome. It is used as follows: after the -T
comes a single letter from the limited set [abdeprw] to select string
prefixes of the tag fields of a game. For instance:

-TaAnnotator - Extract games Annotated by Annotator.

-TbPlayer - Extract games where Player has the Black pieces.

-TdDate - Extract games played on Date.

-TeEco - Extract games with ECO designation Eco.

-TpPlayer - Extract games where Player has either colour.

-TrResult - Extract games with result Result.

-TwPlayer - Extract games where Player has the White pieces.

For example,

pgn-extract -TwTal -TbFischer file.pgn

would extract games from file.pgn in which Tal had the White pieces and
Fischer the Black.

Criteria of the same tag type are or-ed together, so

pgn-extract -Tr1-0 -Tr0-1 file.pgn

extracts only decisive games.

Criteria of different tag types are and-ed together so

pgn-extract -TwTal -Td1962 -Tr1-0 file.pgn

would extract only those games in which Tal played with the White
pieces in 1962 and won.

The ECO classification (see the -e flag)
is performed before attempting to match an ECO tag, so:

pgn-extract -TeA01 -e file.pgn

will perform ECO classification on the input file and extract games
with ECO classification A01 (Nimzo-Larsen attack), for instance.

Argument Descriptions in a File (-A)

It can be inconvenient to repeatedly type long argument lists
on the command line. The -A flag makes it possible to list
arguments in a file, rather than on a command line. Each
argument line within the file must be immediately preceded by
a ':' (colon) character. Consider selecting games by Tal from
a file caro.pgn and writing them to talgames.pgn. Using
command line arguments, this would have the following form:

pgn-extract -TpTal -otalgames.pgn caro.pgn

We can do the same job placing the argument list in the file args:

% Select games by Tal.
:-TpTal
% Where to output the matched games.
:-otalgames.pgn

and the same selection made with:

pgn-extract -Aargs caro.pgn

Note that comments may be included using a '%' character.

Each argument should be listed on its own line, and all the
arguments are available in this way.
The PGN source files may also be listed in the argument file.
They must be listed one per line, with a preceding colon
character. So an alternative for the above would be:

% Select games by Tal.
:-TpTal
% Where to output the matched games.
:-otalgames.pgn
% The game files to be read.
:caro.pgn

and the command invoked as simply:

pgn-extract -Aargs

The -t, -v, -x,
-z, and -R
flags have slightly special treatment in an argument file.
Where the tags, variations, positions, endings and/or roster ordering
are to be read from
files of those names, say, then the format of these arguments in the
argument file might be as you would expect:

:-ttags
:-vvariations
:-xpositions
:-zendings
:-Rroster

However, within an argument file, the file names are optional and,
where omitted, the data that would have been stored in a file for
these flags is listed on lines immediately following.
For instance, an alternative to:

:-TpTal

we could say:

:-t
Player "Tal"

Notice that no colon should be present on the lines following the
flag line.
In the following example, we select games won by Tal as White
reaching a particular position in the Caro Kann:

The arguments file may, itself, also contain -A arguments. This should
make it possible to build up hierarchies of game selection criteria
if desired. However, beware that there is no check for circularities
in the dependencies.

Outputting Games not Matched (-n)

The -n flag will cause all valid games not output via other criteria to
be saved in a given file. The purpose of this is to make it easier to
reorganise files in different ways. For instance, if you wish to remove
all of the games played by Tal from one file, you might do:

pgn-extract -TpTal -otalgames.pgn -nothers.pgn file.pgn

After which, the file others.pgn will contain all of the valid games
from the original file, with the exception of Tal's.

Date Matches with -T

A simple form of relational date matching is available from the command
line (-T).
A date year may be prefixed with either 'b' or 'a' in order
to match games played either before or after the specified date. This
assumes that the date is stored in the game's date tag string in the
normal form: YYYY.MM.DD

So,

pgn-extract -Tdb1962 file.pgn

will look for games played before 1962. A much fuller capability
is available in tag files with the -t flag.

Don't Output Any Tags (--notags)

The tags for a game will not be output.

Suppress annotations in the output (-C -N -V)

If comments (-C or --nocomments),
NAGs (-N or --nonags) and/or variations (-V or --novars) are not required in
the output then these can be suppressed by using one or more of these flags.

Suppressing move numbers (--nomovenumbers)

Move numbers can be suppressed from the output with --nomovenumbers.
Used in combination with
--notags,
--noresults,
-C, -N, and -V
this can be used to output just the moves of a game:

pgn-extract --nomovenumbers --noresults --notags -C -N -V file.pgn

If it is desired to have all the moves on a single line, use the -w flag as well.

Suppressing move numbers (--noresults)

Results at the ends of games and variations
can be suppressed from the output with --noresults.
See suppressing move numbers for a possible use.

Limiting the number of plies output
(--plylimit)

The number of moves (actually plies) output for a game can be limited
by using --plylimit. This must be followed by the maximum
number of plies to be output for a game.
For instance,

pgn-extract --plylimit 10 --nomovenumbers --notags file.pgn

will output games up to a maximum of 10 plies (including variation lines),
without game tags and no line numbers.

Note: If the game has not ended before the ply limit is reached then *
will be used as the terminating result to indicate an incomplete game (see
--noresult for how to suppress this.

Setting bounds on the number of moves in a game (-b)

The -b flag allows you to select games which have a number of moves
within the bounds you set. You can set a lower bound on the number of moves
by using -bl ('l' = lower bound), or an upper limit
by using -bu ('u' = upper bound). Both are followed by
the number of moves so

pgn-extract -bu20 file.pgn

will find brevities of 20 moves or less, whilst

pgn-extract -bl60 file.pgn

will find games of 60 moves or move. Bounds may be combined so

pgn-extract -bl30 -bu40 file.pgn

will find games in the range [30..40] moves. If neither 'l' nor 'u'
is used, but just a number following the -b, this means that the number
of moves must exactly match that number. Alternatively, 'e' can be
used to stand for 'equal to'. The following are equivalent and find
all games of exactly 35 moves.

pgn-extract -b35 file.pgn
pgn-extract -be35 file.pgn

Matching only games that end in checkmate (-M or --checkmate)

The -M flag requests that only games that end in checkmate are matched:

pgn-extract -M file.pgn

Matching only games that end in stalemate (--stalemate)

The --stalemate flag requests that only games that end in stalemate are matched:

pgn-extract --stalemate.pgn

ECO Classification (-e)

A PGN
file of ECO classifications is distributed with this version. I
believe that this was put together by Ewart Shaw, Franz Hemmer and
others, to whom appropriate thanks is due. The -e flag requests
pgn-extract to add/replace ECO classifications in the games it outputs.
This is done by firstly reading a file of ECO lines in PGN format
(eco.pgn in the current directory, by default) and building a table of
resulting positions. As the games are then read they are looked up in
the table to find a classification. The deepest match is found.
A match is allowed within six half moves of the length of the ECO line.
The supplied file has ECO, Opening, and Variation tag strings for many
lines. If present, pgn-extract will add/replace these as well as
SubVariation tags if available.

An alternative file to the default eco.pgn may be supplied in two
ways:

Appending a file name to the -e

-emy_eco_codes.pgn

Note that there must not be a space between the -e and
the name of the file, otherwise the default ECO file will be assumed.

By setting the environment variable ECO_FILE to the full path name
of the file.
Under Windows this can be done with

set ECO_FILE=full-eco-file-path

in at the Cmd window prompt, or more permanently via the
System/Environment/Advanced area.
Under UNIX csh this can be done with

setenv ECO_FILE full-eco-file-path

in the .cshrc, for instance.

Having the ECO data read as plain text on program startup has the
obvious disadvantage that there is a high initial time overhead. On the
other hand, it has the advantage that users may add their own
classifications to the file very easily. It is fairly demanding of
memory, so you advised not to combine this with duplicate detection
(-U,
-D and -d), which can also consume a lot
of memory with big databases.

Because an ECO tag match with either the -t flag or
the -T flag is delayed until after ECO
classification, this makes it relatively easy to select games with
particular ECO codes even if they weren't present in the source form.

Usage of -e with the Seven Tag Roster flag (-7)
results in the ECO
tags (ECO, Opening, Variation, SubVariation) being included in the
output games.

Separate Output Files (-#, -E)

The -# and -E flags permit the output to be split into multiple files.
However, be warned that where the input involves a lot of games,
these flags might result in
the creation of a large number of output files.

The -# flag takes an unsigned integer argument specifying the maximum number
of games to output to a single file. Successive output files are numbered 1.pgn,
2.pgn, etc. Any existing contents of these files are always overwritten on each
run of pgn-extract.

pgn-extract -#250 file.pgn

will check and split file.pgn into separate files of, at most, 250 games each.

pgn-extract -#1 file.pgn

will split file.pgn into separate files containing only a single game each.

The -E flag normally takes a numeric argument of value 1, 2, or 3. This is
used to indicate the level of subdivision required based upon the ECO tag
found in a game.

pgn-extract -E3 file.pgn

will fully subdivide file.pgn into separate files based on the full ECO
code of each game, with names such as B03.pgn, A01.pgn, D45.pgn, etc.
If a game does not contain an ECO tag, or the tag appears to be malformed,
it will be written to a file called, noeco.pgn. All of these files are
written to in append mode, so that existing contents are not lost. However,
beware of using an input file whose name is the same as one that will be
written to by this operation. This could lead to infinite operation.

In fact, values greater than 3 may be used to produce separation of even
finer granularity if more than two digits have been used in the classification
of a game.

Soundex Matching (-S)

There is a simple soundex algorithm available that attempts soundex
matches on White, Black, Site, Event, and Annotator tags if the -S flag
is used in combination with either the -t flag or
the -T flag. The -S flag should
precede all -t and -T arguments. It should be noted that the soundex
matching does produce false matches.

Output Line Length (-w or --linelength)

The -w flag allows an approximate line length to be set for output.
The default value is 75 characters. The following request output
lines to be approximately 100 characters long:

pgn-extract -w100 file.pgn

Output Format and Language (-W)

By default, pgn-extract rewrites the game score into English Standard Algebraic
Notation (SAN) because it is reasonably flexible about the input form
that it will accept. To prevent it from rewriting the original form of
the moves it reads, use the -W flag.

By itself, -W outputs the moves using the input text.

Using -Whalg writes the moves in hyphenated long algebraic (e.g., e2-e4).

Using -Wlalg writes the moves in long algebraic form (e.g., e2e4).

Using -Welalg writes the moves in enhanced long algebraic form (e.g.,
Ne2e4, e5d6ep). The purpose of enhanced long algebraic form is to reduce the
amount of chess-specific knowledge that a post-procesing program might
need in order to interpret a chess game.
For instance, in order to provide a visualisation.

Output using non-English piece letters is possible using a variation
of the -Wsan flag. This flag may have a six-letter suffix indicating
the letters to be used in representing pawn, knight, bishop, rook,
queen and king in game scores and diagrams. So:

pgn-extract -WsanPNBRQK ...

would output in the (default) English notation, and

pgn-extract -WsanBSLTDK ...

would output in German. Note that the letter for a pawn is required because
board positions are sometimes output when an error is detected in
a game score.

-Wepd was introduced in version 15.0 to output in EPD (Extended Position
Description). A game is output as a sequence of EPD descriptions of
the position at the start of the game, and following each move.
Each EPD line contains the FEN board description, the active colour,
castling availability and en passant target square. A c0 comment contains
a synopsis of the player, event, site and date tags from the game's header.

-Wcm is a legacy flag and
outputs the moves in what I believe to be (or used to be) ChessMaster format.

Forsyth-Edwards Notation (FEN) Descriptions (-F)

The -t flag
makes it possible to use Forsyth-Edwards Notation (FEN) in the
description of a position
to be matched. The -F flag provides a convenience method for generating
a suitable FEN description of an arbitrary position.
The -F flag causes pgn-extract to output a FEN description of the final
position reached in a game, within the text of a comment.
For instance, suppose you were interested in finding games that
reach the position after the following moves.

Material Matches (-z)

The -z flag takes a filename of material balances for which you wish to
search in games. The basic structure of the file is one or
more lines of the form

pieces1 pieces2

Pieces1 and pieces2 are lists of English piece letters for the material
for the two sides that you wish to look for in a game.
For instance:

rp nb

looks for an game in which a lone Rook and Pawn for one side are
competing against a lone Knight and Bishop for the other.
The case of the
letters is immaterial, there is no need to include Kings in the
description, and the order of the pieces does not matter. Apart from
Kings, if a piece letter is not listed for a side then then that piece
is not present within that side's material.
A match will be tested for from both White and Black's point of view, so the
example above matches the same games as:

nb rp

Some notation may be added after any piece letter, typically to
indicate something about the number of occurrences of that piece on one
side.

The following are valid for each piece:

* (zero or more of that piece).

+ (one or more of that piece).

d (exactly d occurrences of that piece, where d is a digit).

d+ (d or more occurrences of that piece).

d- (d or fewer occurrences of that piece).

So:

QR2B2N2P8 QR2B2N2P8

is the starting material position, and QR+B*N*P7- represents material
in which we require at least one pawn to be missing from one side and
they should have a Queen and Rook, but we don't care about the minor
pieces.

In addition, some extra notation is available to specify material
relative to the opponent's.
These are placed after the piece letter to which they refer.

= (the number of these pieces must be the same as the opponent's).

# (the number of these pieces must be different the opponent's).

> (the number of these pieces more than the opponent has).

< (the number of these pieces less than the opponent has).

So,

R+P+ R=P#

looks for Rook and Pawn games that with an equal number of Rooks but
unbalanced pawns.

In addition > and < may be preceded by a digit:

d>
(the number of these pieces must be at least d more than the opponent's).

d<
(the number of these pieces must be at least d less than the opponent's).

Two more notations, >=, <= may be preceded by an optional digit
(the default is 1).
The meaning of this may not be intuitively obvious and, to an extent, they
represent a notational compromise.

d>=
(the number of these pieces must be exactly d more than the opponent's).

d<=
(the number of these pieces must be exactly d less than the opponent's).

In this example, both sides have a pair or Rooks but one has exactly one
pawn more than the other:

r2p* r=p1>=

Here is an example where one side has sacrificed a Rook and Pawn for
Knight and Bishop and we don't care whether Queens are on or off the
board, so long as they are balanced:

q*r+n*b*p+ q=r<n>b>p1<

This example represents some of the imprecision that can occur with
matches. The meaning of 'r<' is such that this could match positions
in which one side as 2 Rooks and the other none. This can be corrected
with:

q*r+n*b*p+ q=r1<=n>b>p1<

enforcing strictly one Rook less. We ought also to correct the same
problem with the minor pieces:

q*r+n*b*p+ q=r1<=n1>=b1>=p1<

In practice, we probably want to allow general matching of minor pieces
so the letter 'L' may be used to stand for a minor piece (Bishop or
Knight). This example represents a similar sacrifice of Rook and Pawn for
two minor pieces.

q*r+l*p+ q=r1<=l2>=p1<

I would advise against mixing the minor piece letter with Knight and
Bishop letters in the piece set for a single side, however, as I am not
convinced that it will produce exact results.

Position Stability with -z

The piece sets may be preceded by an optional number indicating the
required stability of the position. Normally, if you are looking for a
position with a particular set of material characteristics then you
probably want that position to last for a reasonable number of moves in
order to study its characteristics. The number before the piece sets is
how many half-moves you wish that material balance to last. By default,
this has a value of 2 so that fleeting positions in the middle of pairs
of exchanges do not produce unwanted matches.
This example looks for double-Rook and pawn games that last at least
10 half-moves:

10 R2P+ R=P*

Text may be added after the piece lists as a form of comment.

A comment line may be placed in a material balance file by using a '%'
as the first character of the line.

The Seven Tag Roster (-7 or --seven)

This flag discards tag pairs that are not part of the Seven Tag
Roster:

Event, Site, Date, Round, White, Black and Result.

However, if the original game included a FEN tag, this is
included in the output, as the moves will make no sense
otherwise. In addition, if the -e flag has been used for ECO
classification, any ECO, Opening, Variation and SubVariation tags
are also output.

User-defined Tag Roster Ordering (-R)

The -R flag makes it possible for to define the order in which
tags for a game are listed in the output.
The flag should be immediately followed by the name of a file
that contains a list of tag names, one per line, for instance:

The '%' character may be used to include comments in the file.
Tags not listed in such a file will appear after the required
tags have been output.

Include a position evaluation after each move (--evaluation)

The --evaluation argument causes a comment to be appended to every move,
which contains an evaluation of the position immediately following that
move.
The default evaluation is a simplified version of
Shannon's board
evaluation. In this case, the evaluation is the difference between the
value of White's position and Black's, where the value of a position is
a weighted sum of the pieces plus a multiplier (0.1) applied to
the number of available moves for that player.

See the evaluate function in apply.c if you wish to
write your own.

Mailing List

I don't run a proper mailing list but if you find the program useful
and would like or to offer suggestions that you think
others might be interested in, then drop me a line at
d.j.barnes@kent.ac.uk

Limitations

The moves, variations, and commentary of each game are held internally
and reformatted when a game is extracted, rather than reproducing the
original text of the game source.

Lower-case 'b' as the first character of a move is taken to be a move
of the b-pawn if one to match the move can be found. Otherwise, Bishop
moves are tried as an alternative. There is no back-up on failure if
picking a valid pawn move was the wrong choice.

Lower-case 'b' as the first character of a Bishop move is not
acceptable in the variations files.

Duplicate detection is not guaranteed to be exact.
The -Z flag has slightly more potential to avoid false duplicates
as it compares separate values for the end position and move sequence,
whereas these are XORed to save space when -Z is not used.
However, this will only make a difference and avoid false
matches if
two different games at the same hashtable index
also produce identical XORed values.

The results of the -x, -v, and -t/-T search criteria are AND-ed
together. There might be occasions when you wanted to search for games
that matched either positional variations or textual variations at the
same time, for instance. This requires multiple runs of pgn-extract.

The -Wsan variation that allows selection of the output language
is tied to single-character piece descriptions. This does
not support Russian usage, for instance, in which the King
is described as a character pair.